Electron radiation temperature measurements in a helium afterglow at 300 K

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Abstract
A high sensitivity, reflection type, X-band radiometer is used to measure the electron radiation temperature in a helium afterglow, at 300 K, in the pressure range from 10 to 80 Torr and for electron densities from 5*1010 cm-3 to 7*1011 cm-3. The common assumption of electron-neutral gas temperature equality is proven false, for electron densities higher than 1011 cm-3. This indicates that extreme care must be taken for the measurement of temperature dependent parameters in the afterglow. The influence of the discharge conditions is shown to be very large on the measured electron temperatures for electron densities higher than 1011 cm-3. Preliminary measurements of atomic metastable density indicate that, for electron density and pressure, the electron temperature is strongly dependent on the metastable to electron density ratio in agreement with theoretical results.